Urethane adhesive cord treatment for power transmission belt and belt

ABSTRACT

A belt with a tensile cord embedded in an elastomeric body, having an adhesive composition impregnating the cord and coating the fibers. The adhesive composition is the reaction product of a polyisocyanate and a polyol, or a polyurethane prepolymer derived therefrom, and a polyamine curative and optionally additional polyol, and with optionally added plasticizer. At least one of the polyisocyanate, the prepolymer, and the polyamine are blocked with a blocking agent. The belt body may be of cast polyurethane, vulcanized rubber, or thermoplastic elastomer. The cord may have an adhesive overcoat.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 12/628,676 filed Dec. 1, 2009, which is hereby incorporatedherein by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

This invention relates generally to a method of treating tensile cordfor reinforcing a belt, the treatment, the cord and the resulting belt,more particularly to a belt with tensile cord reinforcement treated witha blocked urethane adhesive composition, and specifically to a carbonfiber cord impregnated with an amine-cured polyurea-urethane compositionprepared with a blocked component.

Description of the Prior Art

U.S. Pat. No. 5,807,194 to Knutson et al., the contents of which arehereby incorporated herein in its entirety, discloses a synchronouspower transmission belt with a belt body of cast urethane belt material,belt teeth formed of the body, a wear-resistant fabric reinforcementdisposed along peripheral surfaces of the belt teeth, and a tensilemember of helically spiraled cord embedded in the belt body and of ayarn of carbon fiber, wherein there are interstices between the fibersof the cord and belt material penetrates at least a portion of the cordinterstices as the belt is cast so that the cord interstices contain aminimum of about 0.21 mg of belt material per mm³ of cord volume.Penetration of polyurethane elastomer into the cord may give excellentphysical adhesion. However, urethane in its cured state as a highmodulus belt material may make a particular cord material unacceptablewhen it penetrates the interstices of the cord because the so penetratedcord may have an unacceptably high bending modulus. Also, thepenetrating urethane may transfer too high a strain to filamentscomprising the cord and thus cause unacceptable filament breakageresulting in cord failure. Cast polyurethane materials are often of sucha viscosity that it is hard to sufficiently impregnate the cord.Problems from insufficient impregnation include fraying of cord, poorfatigue life, etc.

U.S. Pat. No. 5,231,159 to Patterson et al., the contents of which arehereby incorporated herein in its entirety, describes cast or RIMpolyurethane compositions useful for belts. The polyurethanes are basedon the reaction product of an isocyanate-terminated (preferablypolyether) prepolymer, an amine- or hydroxyl-terminated polyol, and apolyamine or polyol chain extender.

U.S. Pat. No. 6,964,626 to Wu et al., the contents of which are herebyincorporated herein in its entirety, discloses improvedpolyurethane/urea elastomers having high temperature stability to about140-150° C. and low temperature flexibility at about −35-(−40)° C., foruse in dynamic applications. These elastomers are useful for applicationin belts, specifically in automotive timing or synchronous belts,V-belts, multi-V-ribbed or micro-ribbed belts, flat belting and thelike. The polyurethane/urea elastomers are prepared by reactingpolyisocyanate prepolymers with symmetric primary diamine chainextenders, mixtures of symmetric primary diamine chain extenders andsecondary diamine chain extenders, or mixtures of symmetric primarydiamine chain extenders and non-oxidative polyols, which are all chosento eliminate the need for catalysts via standard molding processes, andto improve phase separation. The polyisocyanate prepolymers are reactionproducts of polyols which are nonoxidative at high temperatures, such aspolycarbonate polyols, polyester polyols, or mixtures thereof, withorganic polyisocyanates which are either compact, symmetric andaromatic, such as para-phenylene diisocyanate, 1,5-naphthalenediisocyanate, and 2,6-toluene diisocyanate, or are aliphatic and possesstrans or trans,trans geometric structure, such as trans-1,4-cyclohexanediisocyanate and trans,trans-4,4′-dicyclohexylmethyl diisocyanate.

Prior efforts to treat cord with a softer material to make a moreflexible cord in polyurethane belts have resulted in belts with lowertorque resistance, higher heat build up during flexing, poor resistanceto delamination, and the like. Adhesive treatments for carbon fiber cordin general have been less than adequate for demanding belt applications,whether for polyurethane or rubber belts. Representative of prior carbonfiber adhesive treatments are U.S. Pat. Nos. 6,695,733 and 6,945,891 toKnutson, which disclose a toothed rubber belt withresorcinol-formaldehyde-latex (“RFL”) treated carbon fiber tensile cord.Also representative of the carbon fiber adhesive art is the epoxy primerand RFL treatment of U.S. Pat. No. 4,044,540 to Toki et al., and theprimer and RFL treatment of U.S. Pat. No. 4,978,409 to Fujiwara et al.

U.S. Pat. Appl. Pub. No. 2005-0271874A1 to Sakajiri et al. disclosescarbon fiber sizing treatment with unsaturated urethane compound as theprincipal component. JP 2005-023480A2 to Sakajiri et al. discloses aresin composition including a polyurethane, an epoxy resin and acrosslinking agent for impregnating a carbon fiber bundle.

U.S. Pat. Appl. Pub. No. 2009/0098194A1 describes urea-urethanechemistry.

U.S. Pat. No. 3,962,511 discloses polyurethane compositions forencapsulating textile woven fabric for industrial conveyor belts and amethod of applying a polyurethane reaction mixture in an organic solventsolution.

Reference is made to U.S. Pat. No. 7,824,284 and U.S. Pat. No.7,824,288, the contents of both of which are hereby incorporated hereinin their entireties.

SUMMARY

The present invention is directed to systems and methods which canprovide flexible, high-modulus tensile cords for reinforcing belts andother dynamic rubber articles, including polyurethane power transmissionbelts and rubber drive belts. The present invention can provide a cordwith good adhesion and compatibility with polyurethane belt bodymaterials and with improved handling including excellent tensilestrength, reduced fraying or fly build up, and durability. Polyurethanebelts according to the invention may have improved flexibility forenduring handling, back bending, and the like, and improved cuttingperformance. Rubber belts with carbon tensile cords according to theinvention may exhibit improved performance over conventional RFL-treatedcarbon cord. The invention is directed to cords with an adhesivetreatment that can be applied to a twisted bundle of fibers with goodpenetration into the bundle.

The present invention is directed to a belt with a tensile cord embeddedin an elastomeric belt body with the cord having a polyurea-urethane(“PUU”) adhesive treatment. The PUU adhesive may be based on apolyurethane prepolymer, such as a polyester or polyether orpolycarbonate, terminated with isocyanate, having been derived from apolyol reacted with a diisocyanate, or based on the raw materials forthe prepolymer. The polyester may be polycaprolactone. The polyol may bea mixture of diol and triol. The diisocyanate may be a symmetric,compact diisocyanate, such as PPDI, TDI, MDI, and the like. Thediisocyanate may not be perfectly symmetric, but preferably is. Theadhesive treatment has a polyamine curative. The polyamine may be acompact, symmetric, diamine curative, or a triamine or tetramine. Atleast one of the reactive components of the adhesive treatment may beblocked, providing room temperature stability for the adhesivecomposition along with fast reaction at elevated temperature.Alternatively, both of the polyamine and the prepolymer (or thediisocyanate) may be blocked simultaneously. The invention is alsodirected to the treated tensile cord and the adhesive composition.

In one embodiment of the invention, the polyurethane prepolymer isblocked with a blocking agent such as a pyrazole, a polyketimine, aphenol, a cyclic ketone, a caprolactam, an oxime, or a triazole, Theadhesive composition in this embodiment may further include a polyol ora plasticizer or both in any desired proportion, which may be useful foradjusting the adhesive end properties such as modulus.

In another embodiment of the invention, the polyamine curative is ablocked amine curative, such as an MDA-NaCl complex. The adhesivecomposition in this embodiment may further include a plasticizer whichmay be useful for adjusting the adhesive end properties such as modulus.

In various embodiments, the adhesive composition may further include apolyol, which may be useful for adjusting properties such as modulus,provided the polyol's reactivity with the prepolymer gives sufficientworking time or shelf life.

In an embodiment of the invention, the tensile cord may be based oncarbon fiber filament yarn, which may be twisted before impregnationwith the adhesive. The interstices between the fibers, regardless offiber type, may be partly or completely filled with the adhesive. Thefibers may be coated with the adhesive. The filling may be from 20% to99% or 100% of the volume of the interstices. Though the fibers may becoated and some interstices filled with adhesive, the coating may berelatively thin and not enough to completely bind all the fiberstogether. In an embodiment using cast polyurethane for the belt bodymaterial, the cast polyurethane may impregnate some or all of theremaining interstices and intimately contact the adhesive coating.Alternately, the cord may have an additional overcoat adhesive.

The invention is also directed to a method including the steps of makingan adhesive dip by mixing or dissolving the polyurethane prepolymer orits constituent ingredients in a suitable solvent along with an aminecurative, one of which may be blocked, dipping a yarn or twisted yarninto the dip, drying off the solvent, and at least partially curing theadhesive. During cure, the blocking agent is de-blocked, and urealinkages form between isocyanate end groups on the prepolymer moleculesand the amino end-groups on the amine curative. The prepolymer may belinear (two isocyanate ends) or branched (three or more isocyanate endgroups) (preferably just two or three or mixtures thereof). Theprepolymer may be blocked by adding blocking agent in a solvent beforeadding curative. The amine curative may be blocked by complexing withsalt in a solvent or in a compatible inert plasticizer. Both theprepolymer and the curative may be blocked.

The foregoing has outlined rather broadly the features and technicaladvantages of the present invention in order that the detaileddescription of the invention that follows may be better understood.Additional features and advantages of the invention will be describedhereinafter which form the subject of the claims of the invention. Itshould be appreciated by those skilled in the art that the conceptionand specific embodiment disclosed may be readily utilized as a basis formodifying or designing other structures for carrying out the samepurposes of the present invention. It should also be realized by thoseskilled in the art that such equivalent constructions do not depart fromthe scope of the invention as set forth in the appended claims. Thenovel features which are believed to be characteristic of the invention,both as to its organization and method of operation, together withfurther objects and advantages will be better understood from thefollowing description when considered in connection with theaccompanying figures. It is to be expressly understood, however, thateach of the figures is provided for the purpose of illustration anddescription only and is not intended as a definition of the limits ofthe present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form part ofthe specification in which like numerals designate like parts,illustrate embodiments of the present invention and together with thedescription, serve to explain the principles of the invention. In thedrawings:

FIG. 1 is a fragmented perspective view, with parts in section, of atiming belt constructed in accordance with an embodiment of the presentinvention;

FIG. 2 is a fragmented perspective view, with parts in section, of aV-belt constructed in accordance with an embodiment of the presentinvention;

FIG. 3 is a fragmented perspective view, with parts in section, of amulti-V-ribbed belt constructed in accordance with an embodiment of thepresent invention;

FIG. 4 is a schematic of a flexibility test used to test acharacteristic of a belt embodiment of the invention;

FIG. 5 is a graph of belt tensile strength for several examples and acontrol after back bending three times on a rod of indicated diameter;

FIG. 6 is a graph of example belt lives on Weibull coordinates;

FIG. 7 is a graph of belt tensile strength for two more examples and thecontrol after back bending three times on a rod of indicated diameter;and

FIG. 8 is a graph of belt tensile strength for several more examples andthe control after back bending three times on a rod of indicateddiameter.

DETAILED DESCRIPTION

The present invention is directed to a polyurea-urethane (“PUU”)adhesive composition for use on textile fibers, and in particular forpreparing treated tensile cord for use in reinforced rubber articlessuch as belts or hose. The PUU adhesive is based on a urethane-linkedprepolymer which is then cured with amines or water to form urealinkages. The PUU adhesive may be preferably amine cured, rather thanbeing moisture cured. Preferably one of the reactants is blocked. ThePUU adhesive may be preferably based on a prepolymer of para-phenylenediisocyanate (“PPDI”) and a polycaprolactone (“PCL”). The PUU-treatedcord is particularly advantageous in polyurethane (“PU”) and/or PUUbelting or other polyurethane articles, whether cast elastomer orthermoplastic elastomer. With a suitable overcoat adhesive, thePUU-treated cord is also suitable for use in rubber belting, hose, orother vulcanized rubber articles. The fiber of the treated cord maypreferably be carbon fiber.

The PUU adhesive may be based on a polyurethane prepolymer, such as apolyester or polyether or polycarbonate terminated with isocyanate. Suchprepolymers are made by reacting a polyisocyanate, with a polyol (i.e.,an hydroxy-terminated polymer, a diol and/or triol preferably).Alternately, the adhesive may be based on the polyisocyanate and thepolyol instead of the prepolymer. Preferably the polyisocyanate is asymmetric, compact diisocyanate, such as PPDI, 2,4- and/or 2,6-toluenediisocyanate (“TDI”), 4,4′-methylene diphenyl diisocyanate (“MDI”), etc.The polyisocyanate may not be perfectly symmetric, but preferably issymmetric. The PU prepolymer may then be dissolved in a suitable solventalong with small or compact, symmetric, di- or poly-amine curative/chainextender or with water alone which may simply be available from ambientmoisture present in the solvent and/or the air, which after drying thesolvent, react to form urea linkages between isocyanate end groups onthe prepolymer molecules. The prepolymer may be linear (i.e. with twoisocyanate end groups) or branched (i.e. with three or more isocyanateend groups), but is preferably with just two or three isocyanate endgroups or mixtures or blends thereof. The urea linkages/segmentsaggregate to form hard-segment domains interspersed throughout a softsegment matrix of polyester, polyether, etc. For a belt cordapplication, it has been found advantageous to make the adhesive softerthan the belt body material, so small, compact curatives are preferred.The most preferable curative is water, giving the smallest hard segmentand therefore the softest PUU adhesive. The most preferable soft segmentfor belt applications is a polyester such as polycaprolactone because ofits excellent heat resistance, tear resistance, etc. Polyethersgenerally have a lower tear resistance than polyesters. Resistance totear can be very important in reinforced rubber articles such as belts,especially at the interface between the cord and the body of the articleor the tooth compound of the belt. The most preferable diisocyanate forbelt applications is PPDI because of its thermally stable linkages, andbecause it has the best reactivity with curatives such as water. Cordsmade with the preferred PUU are extremely flexible after being dipped ortreated, and thus partially or fully impregnated with PUU. As a result,the treated cords exhibit minimal handling damage during processing andend use, and they bond well to various cast PU or PUU belt bodyformulations, to thermoplastic elastomers (“TPE”s), and thermoplasticpolyurethanes (“TPU”s), and to rubber in vulcanized rubber belts. Forsome applications, bonding may be enhanced with suitable overcoatadhesives.

The general term “polyurethane” (PU) may be commonly used in the art toinclude polyureas, polyisocyanurates, and other polymers which may havelittle or no actual urethane groups or linkages. Herein, “polyurethane”is used in a more literal sense to refer to polymers which are reactionproducts of isocyanates and alcohols and thus contain significantamounts of urethane linkages, —NR—CO—O—. Herein and in the claims,“polyurea” is used to refer to polymers which are reaction products ofisocyanates with themselves in the presence of moisture or water, orreactions of isocyanates with amines which may be reactionintermediates, resulting in significant amounts of urea linkages,—NR′—CO—NR″—. In these urethane or urea linkages, R, R′, and R″ are eachindependently hydrogen; alkyl, or aryl groups. Included in the term“polyurea” are biurets, which are formed when a urea group reacts withadditional isocyanate to form a branched polymer. “Polyisocyanurate” isused to refer to polymers which are reaction products of isocyanateswith themselves at elevated temperatures to form a tri-isocyanurate ringstructure. The terms, polyurea and polyurethane, are not meant to implytotal purity of reaction, but are used to indicate what is believed tobe the dominant reaction mechanism and/or reaction product involved inthe inventive adhesive system. Thus, minor amounts of other reactionproducts or other reaction mechanisms may be involved without furthermention in what may still be referred to herein as a predominantlypolyurea-urethane reaction product. The term “polymer” will beunderstood to include polymers, copolymers (e.g., polymers formed usingtwo or more different monomers), oligomers (i.e., polymers withrelatively few repeat units), and combinations thereof, as well aspolymers, oligomers, or copolymers that can be formed in a miscibleblend. The term “pre-polymer” refers to a monomer or system of monomersthat have been reacted to an intermediate molecular weight state. Thismaterial is capable of further polymerization by reactive groups to afully cured high molecular weight state. As such, mixtures of reactivepolymers with unreacted monomers may also be referred to aspre-polymers. Typically such prepolymers are polymers of relatively lowmolecular weight, usually between that of the monomer and that of thefilm polymer or resin. As such, one of skill in the art will appreciatethat monomers react to form the polyurea-urethane such that the monomeris no longer present once the polymer is formed. However, in somecompositions described herein, both monomer and polymer may be presentin the formulation prior to curing. The term “polyamine” is meant torefer to compounds having at least two (primary and/or secondary) aminefunctional groups per molecule. The term “polyol” is meant to refer tocompounds having at least two hydroxyl functional groups per molecule.The term “diol” is meant to refer to compounds having two hydroxylfunctional groups per molecule. The term “triol” is meant to refer tocompounds having three hydroxyl functional groups per molecule. The term“polyisocyanate” and “polyisothiocyanate,” collectively referred to as“polyiso(thio)cyanate” are meant to refer to compounds having at leasttwo isocyanate or isothiocyanate, respectively, functional groups permolecule. The term “diisocyanate” is meant to refer to compounds havingtwo isocyanate functional groups per molecule.

The polyurethane prepolymers useful in embodiments of the invention maybe made by reacting a polyol with a polyisocyanate according to methodsknown in the art. Useful polyols include but are not limited topolyester polyols, polyether polyols, polythioether polyols,polycarbonate polyols, and polycaprolactone polyols. Polycaprolactonesmay be considered types of polyesters. Preferred polyols forapplications requiring thermal stability are nonoxidative up to 150° C.,and include but are not limited to polyester polyols, polycaprolactonepolyols, and polycarbonate polyols. The polyester polyols used in thepresent invention include but are not limited to reaction products ofpolyhydric alcohols, preferably dihydric alcohols with the addition ofsome trihydric alcohol, and/or polybasic carboxylic acids, preferablydibasic carboxylic acids with the addition of some tribasic carboxylicacids. The corresponding polycarboxylic acid anhydrides or correspondingpolycarboxylic acid esters of lower alcohols or mixtures thereof arepreferred over their free polycarboxylic acid counterparts for preparingthe polyesters. The polycarboxylic acids may be aliphatic,cycloaliphatic, and/or aromatic in nature. The following are mentionedas non-limiting examples: succinic acid, adipic acid, suberic acid,azelaic acid, sebasic acid, phthalic acid, isophthalic acid, trimelliticacid, phthalic acid anhydride, tetrahydrophthalic acid anhydride,hexahydrophthalic acid anhydride, tetrachlorophthalic acid anhydride,endomethylene tetrahydrophthalic acid anhydride, endomethylenetetrahydrophthalic acid anhydride, glutaric acid anhydride, fumaricacid, dimeric and trimeric fatty acids, optionally mixed with monomericfatty acids, dimethylterephthalate and terephthalic acid-bis-glycolesters. Suitable polyhydric alcohols used to produce such polyestersinclude but are not limited to the following; ethylene glycol, 1,2- and1,3-propylene glycol, 1,4- and 2,3-butylene glycol, 1,6-hexanediol,1,8-octanediol, 1,10-decanediol, neopentyl glycol, 1,4-cyclohexanedimethanol or 1,4-bis-hydroxymethylcyclohexane,2-methyl-1,3-propanediol, glycerol, trimethylopropane (“TMP”),1,2,6-hexanetriol, 1,2,4-butanetriol, trimethylolethane, and mixturesthereof. Polyesters of lactones, such as ε-caprolactone, andhydroxycarboxylic acids, such as omega-hydroxycaproic acid, may also beused.

Suitable polycarbonate polyols are known and may be prepared, forexample, by the reaction of diols, such as 1,3-propanediol,1,4-butanediol, 1,6-hexanediol, 1,10-decanediol, neopentyl glycol,diethylene glycol, triethylene glycol or tetraethylene glycol, andmixtures thereof, with diaryl carbonates, e.g. diphenyl carbonate,dialkyl carbonate, e.g. diethyl carbonate, or phosgene. Suitablepolyether polyols are known and include hydroxyl-terminated polyetherssuch as those based on alkylene oxides which includes propylene oxide(PPO), ethylene oxide, and polytetramethylene oxide (PTMO). Thepreferred alkylene oxide is a polypropylene oxide. The polyol may be apolyether polyol having an average hydroxyl functionality of from about2 to 8 with an average hydroxyl equivalent weight of from about500-5000, or a polyether polyol hydroxyl functionality of from about 2to 4 with an hydroxyl equivalent weight of approximately 1000-3000. Inan embodiment, the polyether polyol includes an average hydroxylfunctionality of from about 2-3 with an average hydroxyl equivalentweight of approximately 1500-2500.

Preferred polyols are polycarbonate polyols and polyester polyols withmolecular weights from about 500 to about 4000 or 5000, or mixtures ofthese polyols. The more preferred polyols are poly(hexamethylenecarbonate) (“PCB”) diol and/or triol, polycaprolactone (“PCL”) dioland/or triol, and poly(hexamethylene adipate) diol and/or triol withmolecular weights from about 300 or 500 to about 4000 or 5000. The mostpreferred polyols for treating tensile cords for belts and hose arepolycaprolactone diols and/or triols. The most preferred molecularweights for diols range from about 1500 to about 2500 and for triolsrange from about 1000 to about 4000, or from about 2500 to about 3500.The polyols are dried to a moisture level of less than about 0.03% byweight, and more preferably, to a level of about 0.0150% by weight priorto reaction with the diisocyanates to form the polyisocyanateprepolymers useful for this invention. The polyol used to prepare theprepolymer may be a mixture of at least one triol selected from theabove polyols and one or more other polyols, preferably diols. The mostpreferred diols and triols are the most preferred polyols listed above.The amount of triol crosslinker in the polyol mixture is notparticularly limited since it is possible to use anywhere from about 2%up to 100% triol. Nevertheless in preferred embodiments, the amount oftriol in the polyol mixture may preferably be from 5% up to about 65% byweight of the total polyol component of the prepolymer, more preferablyfrom about 15% to about 55%. The remainder of the polyol mixture may bediol. Too little triol leads to insufficient crosslinking and little orno improvement in high temperature performance, while too much triolleads to processing or mixing difficulties from the increase inviscosity of the prepolymer and/or lack of wetting or penetration oftextile reinforcement by the polyurethane and/or chemical instability ofthe mixture. In embodiments of the invention, the prepolymer may beprepared by mixing a diol-based prepolymer with a triol-basedprepolymer. However, the increased viscosity of triol-based prepolymersmakes this difficult. Thus, a preferred embodiment is a prepolymerprepared from a mixture of diol and triol, preferably PCL polyols.

Useful polyisocyanates for preparing the prepolymers include but are notlimited to para-phenylene diisocyanate (“PPDI”), 2,4- and/or 2,6-toluenediisocyanate (“TDI”), 4,4′-methylene diphenyl diisocyanate (“MDI”),hexamethylene diisocyanate (“HDI”), 1,5-naphthalene diisocyanate(“NIDI”), trans-1,4-cyclohexane diisocyanate (“t-CHDI”), trimethylxylylene diisocyanate (“TMXDI”), isophorone diisocyanate (“IPDI”) andthe like, and mixtures thereof. The organic polyisocyanates suitable forthe polyisocyanate prepolymers used in the present invention arepreferably those possessing the following characteristics: compact andsymmetric structure for aromatic compounds, or trans or trans,transgeometric structure for aliphatic compounds, for improved phaseseparation of the resulting elastomers, and high reactivity with aminegroups or water to eliminate the need for catalysts in the formulations,which otherwise accelerate reversion of the resulting elastomers at hightemperatures. Polyisocyanates preferred as starting components for thepreparation of the polyurethane prepolymers include but are not limitedto compact, symmetric aromatic diisocyanates, including but not limitedto PPDI, NIDI, and 2,6-toluene diisocyanate (“2,6-TDI”). Thepolyisocyanates useful as starting components for the preparation of thepolyisocyanate prepolymers also include cycloaliphatic diisocyanateswith trans or trans,trans geometric configuration. These isomers aregenerally pure, i.e., they exist in the substantial absence ofcis-configured isomers, and thus promote good phase separation oncecured. These include but are not limited to t-CHDI, andtrans,trans-4,4′-dicyclohexylmethyl diisocyanate (“t,t-HMDI”). Mostpreferred for use in embodiments of the present invention in reinforcingtensile cords for belts and hose is PPDI.

The chain extenders (i.e. curatives) useful in the present invention areselected so as to be capable of adequate reaction time with theprepolymer, and to give the desired urea linkages, with a desired amountof phase separation and hard segment properties. The chain extender mayinclude a compound of aliphatic amines, aromatic amines and mixturesthereof. The chain extender may include an aliphatic amine such asethylene diamine, 1,3-diaminopropane, 1,4-diaminobutane,hexamethylenediamine, aminoethanolamine, 1,4-diaminocyclohexane,isophorone diamine (“IPDA”) and triethylenetetramine. The chain extendermay preferably be an aromatic amine which may include2,4-diaminotoluene, 2,6-diaminotoluene, 1,5-napthalenediamine,1,4-phenylenediamine, 1,4-diaminobenzene, 4,4′-methylenebis(orthochloroaniline) (“MOCA”), 4,4′-methylenebisdianiline (“MDA”),3,5-diethyl-2,4-diaminotoluene, diethyl toluene diamine (“DETDA”),trimethyleneglycol diaminobenzoate (“TMGDAB”),4,4′-methylenebis(3-chloro-2,6-diethylaniline) (“MCDEA”),4,4′-methylenebis(2,6-diethylanaline) (“MDEA”), and3,3′,5,5′tetraisopropyl-4,4′-methylenebisaniline. Preferred chainextenders are small, compact and symmetric aromatic diamines. Preferablythe curative has no more than two phenyl rings and/or no longer than athree-carbon aliphatic group. In one embodiment, the chain extender iswater, including for example ambient moisture. Water forms the mostcompact of the urea linkages, —NH—CO—NH—. The simple urea linkagesformed by the reaction with water as the curative minimize the size ofthe hard segment domains, while still giving good phase separation andphysical properties. This leads to good flexibility of the resultingtreated fibers or tensile cords, as desired for use in dynamic rubberapplications like belts and hose. Moreover such a small hard segmentbased on water, in combination with a small symmetric diisocyanate, suchas PPDI, results in a good overall balance of properties includinghigh-temperature stability, flexibility, modulus and strength. However,water may react slower than desired and the treated cord may remain tootacky for too long. Therefore, polyamine curatives may be preferable.

Symmetric primary diamine chain extenders useful in the preparation ofpolyurea-urethane adhesive in accordance with an embodiment of thepresent invention are those capable of reacting with polyisocyanateprepolymers rapidly without the need for catalysts. The symmetry of thechain extenders useful in an embodiment of the present inventionprovides improved phase separation and hence increase the thermalstability of the final PUU elastomers in dynamic applications. Suitableprimary diamine chain extenders include but are not limited to symmetricaromatic amines with molecular weights of from about 90 to about 500,and mixtures thereof. Examples include: 1,4-phenylenediamine,2,6-diaminotoluene, 1,5-naphthalenediamine, 4,4′-diaminodiphenylmethane, 3,3′-dimethyl-4,4′-diaminodiphenyl methane,1-methyl-3,5-bis(methylthio)-2,6-diaminobenzene,1-methyl-3,5-diethyl-2,6-diaminobenzene,4,4′-methylene-bis-(3-chloro-2,6-diethylaniline) (MCDEA),4,4′-methylene-bis-(ortho-chloroaniline),4,4′-methylene-bis-(2,3-dichloroaniline), trimethylene glycoldi-para-aminobenzoate, 4,4′-methylene-bis-(2,6-diethylaniline) (MDEA),4,4′-methylene-bis-(2,6-diisopropylaniline),4,4′-methylene-bis-(2-methyl-6-isopropylaniline), 4,4′-diamino diphenylsulfone, and the like. The symmetric primary diamine chain extenders mayoptionally be combined with a small amount of secondary diamine chainextenders in order to vary elastomer characteristics such as hardness.Suitable examples of secondary diamine chain extenders have molecularweights of from about 150 to about 500, and include but are not limitedto N,N′-di-sec-butyl-amino benzene andN,N′-di-sec-butyl-amino-diphenylmethane.

It may be advantageous to block one or more of the reactive components,namely the polyisocyanate, the prepolymer or the curative, in theinventive adhesive composition. Blocking (also called capping) refers toattaching a blocking agent to a reactive group such as the isocyanateend groups of the polyisocyanate or prepolymer or the amine groups of adiamine curative, wherein the blocking agent prevents the reactive groupfrom engaging in its usual reactions at room temperature, but readilydissociates at an elevated temperature making the reactive groupsavailable again for the usual reactions.

It may be advantageous to block the isocyanate groups in the prepolymer.Suitable blocking reagents include polyketimines, phenols, cyclicketones, caprolactam, oximes, triazoles, certain alcohols, andβ-dicarbonyl compounds such as ethyl acetoacetate and ethyl malonate. Apreferred blocking agent is methyl ethyl ketoxime (“MEKO”). Usefulphenols include nonyl phenols (e.g., p-nonyl phenol), butyl phenols(e.g., p- or o-tert butyl phenol), dodecylphenols, propyl phenols,heptyl phenols, octyl phenols, cresols, trimethylphenols, xylenol, andthe like. Other preferred blocking agents include 3,5-dimethylpyrazole(“DMP”), diethylmalonate (“DEM”), ε-caprolactam (“ε-CAP” or simply“CAP”), 1,2,4-triazole, dimethyl-1,2,4-triazole, imidazole,diisopropylamine, acetoacetic ester. Useful oximes include acetophenoneoxime, acetone oxime, methyl ethyl ketoxime, cyclohexanone oxime, propylaldehyde oxime, formaldoxime, butyl aldehyde oxime, cyclopentanoneoxime, benzophenone oxime, and butanone oxime. Mixtures of blockingagents may be used. The equivalents ratio of isocyanate groups toblocking agents in the starting materials used to prepare the blockedpolyurethane prepolymer may also be varied as desired. In certainembodiments, the NCO equivalents to blocking agent ratio may be withinthe range of from 1:1.01 to 1:1.20, preferably 1:1.03 to 1:1.10, orpreferably about 1:1.05.

According to an embodiment of the invention, the dip solution mayinclude blocked isocyanate prepolymer(s), and diamines or aliphaticprimary or secondary triamine(s) or tetramine(s) in appropriate molarratio, and optionally, plasticizers, oligomeric polyamines, or polyols,all in an organic solvent solution. All of these listed amine optionsare considered included in the term “polyamines.” The amines can reactspontaneously with the de-blocked isocyanate prepolymer at elevatedtemperature and result in a fast-drying polyurethane-urea treatment. Theaddition of one or more of plasticizers, oligomeric polyamines, orpolyols into the formulation can lower the film modulus and improve thetensile cord flexibility, resulting in better belt backbend resistance.It should be noted that adhesive properties may be determined by castinga suitable film for testing, such as for hardness and tensile modulus,elongation, and strength.

Suitable blocked isocyanate prepolymers include Adiprene BLFP2950A,Adiprene BLM500, and Adiprene BL16, sold under the Adiprene trademark byChemtura Corporation; also Trixene “BI grades” sold under the Trixenetrademark by Baxenden Chemicals Ltd. including Trixene BI-7641; alsoDesmodur BL 1100/1, sold under the Desmodur trademark by Covestra.Similar blocked prepolymers with lower NCO would be preferred forlowering film modulus. Higher NCO prepolymers will generally give higherfilm modulus, which can be adjusted downward by adding plasticizers,polyols, etc. Note that polyols are too reactive with isocyanates to usein solution with prepolymers that are not blocked. The blocking of theprepolymer thus permits additional formulation choices for the adhesivecomposition.

Suitable aliphatic primary or secondary triamine or tetramine curativesfor use with blocked prepolymers include Jeffamine T-5000, JeffamineT-403, Jeffamine ST-404, and Jeffamine XTJ-616, sold under that tradename by Huntsman Corporation. The amine functionality of three or four(greater than two) may provide faster curing and drying and lowermodulus for the treatment film than diamine functionality.

Instead of blocking the prepolymer for use with diamine curatives, itmay be advantageous to use one or more blocked diamine curatives. Thediamine curative may be blocked for example by complexing with salt in asolvent or in a compatible inert plasticizer. Examples of blockeddiamines include: tris (4, 4′-diamino-diphenyl methane) sodium chloride(an MDA-NaCl salt complex dispersed in a plasticizer), such as thosesold under the trade names Caytur 31, Duracure C3LF, and Duracure C3 byChemtura. Ketimines can also be considered blocked amines and may beuseful. It may be noted that both the prepolymer and the curative may beblocked.

The amount of polyamine to add may be the stoichiometric amount to reactwith all available isocyanate end groups on the prepolymer, or somewhatmore or less. Using somewhat less than the stoichiometric amount ofpolyamine may encourage some crosslinking which may be beneficial insome applications. When additional polyol is included in the adhesivecomposition, then the amount of polyamine may be reduced accordinglysince the polyol will react with the isocyanate end groups on theprepolymer. The molar ratio of reactive amine groups plus active alcoholgroups on the additional polyol to the number of isocyanate groups onthe prepolymer may thus advantageously be selected to be in the rangefrom 0.8 to 1.1, preferably from 0.9 to 1.0.

Plasticizers may be incorporated for lower film modulus. Examples ofuseful or suitable plasticizers include phthalates, organo-phosphates,dialkyl-ether di-alkylesters and polyalkylene-ether di-alkylesters, suchas di- or poly-ethylene glycol di-alkylesters. Dialkyl-ether diestersinclude C₄ to C₁₂-esters of C₁- to C₄-ether- or polyether-dicarboxylicacids. Examples of such plasticizers may include esters such as caprate,caprylate, hexanoate, heptanoate, pelargonate, 2-ethylhexoate, and thelike. Examples of such plasticizers may include di-alkylesters of etherssuch as ethylene glycol, propylene glycol, triethylene glycol,tetraethylene glycol, and polyethylene glycols (“PEG”) having amolecular weight of up to about 800. Useful, non-limiting examples ofcommercial phthalate-type and ester-type plasticizers include those soldunder the trade names Palatinol® by BASF, Jayflex™ by ExxonMobile, andTegmer® by Hallstar.

Polyols can be used to adjust the hardness or modulus of the adhesive,but only if the prepolymer or polyisocyanate is blocked to prevent earlyreaction between prepolymer or polyisocyanate and polyol in thesolution. Suitable polyols may include one or more of the aforementionedpolyols. Some preferred polyols are the same ones mentioned above foruse in forming the prepolymer.

Oligomeric polyamines can also be used to adjust the hardness or modulusof the adhesive. The useful polyamines may be the same as the polyolsmentioned above, but with the hydroxyl groups replaced by amine groups.Such polyamines may advantageously react faster than the equivalentpolyols, result in faster curing/drying formulations and thereforefaster processing or treating of tensile cord. Exemplary oligomericpolyamines include polyoxypropylenediamine, available as JeffamineD-2000 from Huntsman Corporation.

The present invention may also utilize various other additives in orderto assist in the processing of a product from the composition of theinvention or to assist in the functioning of a product made from theelastomer of the invention, including antioxidants, other plasticizers,fillers, colorants, adhesion promoters, co-reactants, chain extenders,and the like. For example, antioxidants are particularly useful when theelastomeric composition of the present invention is utilized in a powertransmission belt product. Suitable antioxidants include2,6-di-t-butylphenol and polyalkylene glycol esters of hindered phenolsof substituted alkanoic acids. Examples of antioxidants include3,5-di-t-butyl-4-hydroxybenzoic acid ester of ethylene glycol,bis{3-(3-methyl-5-t-butyl-4-hydroxyphenyl) propionate} of trimethyleneglycol. Other polyols, polyisocyanates, isocyanate-terminated polymers,epoxies, and/or amines may be included for example, as adhesionpromoters, co-reactants, though preferably they are not included.

Other added compounds may be useful with the composition of the presentinvention. These include catalysts to decrease the reaction time of thecomponents. The catalysts may be selected from any desirable compoundknown in the art such as organo-metal compounds, tertiary amines, andalkali metal alkoxides. However, the polyurea-urethanes can be preparedwith or without catalysts, whereas polyurethanes based on polyols whichdo not contain amine terminated groups are most typically prepared witha catalyst. Suitable organo-metal compounds useful as catalysts includebut are not necessarily limited to aliphatic soaps of tin, mercury,iron, zinc, bismuth, antimony, cobalt, manganese, vanadium, copper andthe like. Examples include organic ligands which are carboxylic acids of2-20 carbons, such as dibutyl tin dilaurate, dimethyl tin dilaurate,phenylmercuric propionate, copper naphthenate, bismuth neodecanoate, andthe like. In a preferred embodiment, no catalyst is used.

Thus, a preferred embodiment of an adhesive composition according to theinvention comprises as the only reactive ingredients the polyurethaneprepolymer and a polyamine curative. In certain applications, the use ofwater alone as the curative may result in a cure rate that is slowerthan desired, and the use of diamine curative may result in an adhesivemixture with less shelf stability than desired. Use of a blockedcomponent in the adhesive composition according to an embodiment of theinvention may provide both an acceptable shelf stability and a suitablyfast cure rate. The blocked component may be either the polyurethaneprepolymer or the polyamine curative, and in either case, water is notrelied on as the curative. Surprisingly, it has also been found that useof a blocked component can also lead to improved product performance aswill be seen in certain examples below.

Throughout the present disclosure, the term “cord treatment” is used todenote a material applied to a yarn and/or yarn filament (which may ormay not include a sizing) and which ends up located at least on aportion of the yarn and/or yarn filament surface or sized surface andwithin at least a portion of one or more interstices formed between suchfilaments and yarns. The cord treatments disclosed herein are considereddistinct from any sizing present on the yarn or filaments.

Many polyisocyanate prepolymers are commercially available and may bebeneficially employed in the practice of one or more embodiments of thepresent invention; and include those generally referred to as “low free”prepolymers as described for example in U.S. Pat. No. 6,174,984 toPeter, U.S. Pat. No. 5,703,193 to Rosenberg, U.S. Pat. Pub. No.2003/0065124 to Rosenberg et al., and U.S. Pat. No. 6,046,297 toRosenberg et al., in which the level of free diisocyanate in theprepolymer is reduced to a level of, e.g., less than 1% of theprepolymer, or less than 0.5%, or less than 0.25%, e.g., about 0.1% orlower.

Suitable isocyanate-terminated prepolymers for carrying out theinvention include the following available on the market. For example, anumber of useful prepolymers are available under one or more of theADIPRENE®, DURACAST, and VIBRATHANE® trademarks from ChemturaCorporation, including Adiprene® LFP 2950A, a preferredlow-free-monomer, PPDI-terminated polycaprolactone prepolymer; Adiprene®LFP 3940A, a PPDI-terminated polycarbonate prepolymer; Adiprene® LFP1950A, a PPDI-terminated polyester prepolymer; Adiprene® LF 1950A, aTDI-terminated polyester prepolymer, and Adiprene® LFP 950A, aPPDI-terminated polyether prepolymer; Adiprene LF 1600D, LF 1700A, LF1800A, LF 1860A, and LF 1900A, are useful low-free-monomer,TDI-terminated polyester prepolymers; and Adiprene® LF 600D, LF 750D, LF753D, LF 800A, LF 900A, LF 950A, LFG 740D, LFG 920, and LFG 964A areuseful low-free-monomer, TDI-terminated polyether prepolymers; Adiprene®LFM 2450, Duracast™ C930, and Vibrathane® 8030 and 8045 are usefulMDI-terminated polycaprolactone prepolymers; Adiprene® LFH 120, 2840,3520, and 3860 are useful HDI-terminated prepolymers. Useful prepolymersare also available under one or more of the trademarks VULKOLLAN® andBAYTEC® from Covestra; under the TECHTHANE® trademark from Trelleborg;under the IMUTHANE® and/or VERSATHANE® trademarks from COIM USA, Inc.;ANDUR® from Anderson Development Company; polyurethane prepolymers soldunder the ECHELON™ trademark from Dow; and so on.

Suitable blocked-isocyanate prepolymers may be prepared from suitableisocyanate-terminated prepolymers for carrying out the invention byadding the prepolymer and the blocking agent to an organic solvent andreacting under suitable conditions. Preferably a small excess ofblocking agent is used to ensure complete blocking of the isocyanate endgroups. The suitable conditions depend on the volatility and reactivityof the chosen ingredients. Generally, blocking may be done in solutionat room temperature with stirring. The blocking reaction may beaccelerated by adding heat, for example, heating the solution up toabout 70° C. or 80° C.

Referring to FIG. 1, a typical timing belt 10 is illustrated. Belt 10includes elastomeric main body portion 12 and sheave contact portion 14positioned along the inner periphery of main body portion 12. Thisparticular sheave contact portion 14 is in the form of alternatingtransverse teeth 16 and land portions 18 which are designed to mesh witha transverse-grooved pulley or sprocket. Tensile layer 20 is positionedwithin main body portion 12 for providing support and strength to belt10. In the illustrated form, tensile layer 20 is in the form of aplurality of tensile cords 22 aligned longitudinally along the length ofmain body portion 12. It should be understood that, in general, any typeof tensile layer 20 known to the art may be utilized. Moreover, anydesired material may be used as the tensile member, such as cotton,rayon, polyamide, polyester, aramid, steel, glass, carbon, PBO,polyketone, basalt, boron, and even discontinuous fibers oriented forlow load carrying capability, or hybrids thereof. In the embodiment ofFIG. 1, tensile layer 20 is in the form of illustrated tensile cords 22made from one or more yarns of high-modulus fiber, twisted or pliedtogether into a cord and treated with the PUU adhesive treatmentdescribed herein. Preferred high-modulus fibers include carbon,polyethylene naphthalate (PEN), poly(p-phenylene-2,6-benzobisoxazole)(PBO), aramid, basalt, boron, or liquid crystal polymer (LCP). In apreferred embodiment, the cords 22 comprise aramid or carbon fiber. Morepreferably, the cord may be a twisted filament yarn, or a twisted bundleof yarns of continuous carbon filaments.

By aramid is meant a long chain synthetic polyamide having its amidelinkages attached directly to two aromatic rings in either the para ormeta position. In the present invention, use may be made, for example,of PPD-T, poly(p-benzamide), copoly(p-phenylene/3,4′-oxydiphenyleneterephthalamide), or the like. By PPD-T is meant the homopolymerresulting from mole-for-mole polymerization of p-phenylene diamine andterephthaloyl chloride and, also, copolymers resulting fromincorporation of small amounts of other diamines with the p-phenylenediamine and of small amounts of other diacid chlorides with theterephthaloyl chloride. Commercial aramid fibers suitable for thepractice of this invention include those sold under the trademarksTEIJINCONEX, TECHNORA, and TWARON by Teijin Limited, and under thetrademarks NOMEX, and KEVLAR by E.I. DuPont de Nemours and Company.

Reinforcing fabric 24 may be utilized and intimately fits along thealternating teeth 16 and alternating land portions 18 of belt 10 to forma face cover or tooth cover for the sheave contact portion. This fabricmay be of any desired configuration such as a conventional weaveconsisting of warp and weft threads at any desired angle or may consistof warp threads held together by space pick cords, or of a knitted orbraided configuration, or a nonwoven fabric, and the like. More than oneply of fabric may be employed, or combinations of different fabrictypes. If desired, fabric 24 may be cut on a bias so that the strandsform an angle with the direction of travel of the belt. Conventionalfabrics may be employed using such materials as cotton, polyester,polyamide, acrylic, aramid, polyketone, hemp, jute, fiberglass, andvarious other natural and synthetic fibers including blends orcombinations thereof. In a preferred embodiment of the invention, fabriclayer 24 consists of an expansible wear-resistant fabric in which atleast one of the warp or weft threads is made of nylon. In the preferredform, fabric layer 24 is made from a nylon 66 stretch fabric, andpresents an elastomer-free (polyurethane/urea-free) surface for engagingcooperating drive sheaves. The elastomer-free surface may include apolymeric film laminated to the fabric. The fabric may also be treatedwith the inventive PUU cord adhesive if desired.

Referring to FIG. 2, standard notched V-belt 26 is illustrated therein.V-belt 26 includes an elastomeric body portion 12 similar to that ofFIG. 1 and tensile reinforcement layer 20 in the form of cords 22, alsosimilar to that as illustrated in FIG. 1. The elastomeric body 12,tensile layer 20, and cords 22 of V-belt 26 may be constructed from thesame materials as described above for FIG. 1. It should be noted thatthe tensile layer 20 may optionally include an elastomeric compositionor rubber material that is different than the rest of the main bodyportion in order to provide a transitional layer in terms of modulus orother property and/or to function as an adhesive layer between cord andmain body. The optional adhesive rubber member may for example be ofhigher modulus than the main body as described in U.S. Pat. No.6,616,558 to South, the contents of which are hereby incorporated hereinby reference.

V-belt 26 also includes sheave contact portion 14 as in the powertransmission belt of FIG. 1. In this embodiment, however, sheave contactportions 14 are the two juxtaposed sides of the belt, designed to wedgeinto a V-sheave. The bottom surface of V-belt 26 is in the form ofalternating notch depression surfaces or troughs 28 and projections 30.These alternating notched depression surfaces 28 and projections 30 mayfollow a generally sinusoidal path as illustrated which serves todistribute and minimize bending stresses as the sheave contact portion14 passes around pulleys and sheaves. Various notch profiles thatdeviate from sinusoidal in various ways are also useful. However,troughs 28 and projections 30 are optional. Included in the category ofV-belts are those V-belts designed for continuously variabletransmission (“CVT”) applications, which often exhibit a belt bodyrelatively wider than the belt thickness.

Referring to FIG. 3, multi-V-ribbed belt 32 is illustrated.Multi-V-ribbed belt 32 includes main elastomeric body portion 12 as inthe belts of FIGS. 1 and 2 and also includes tensile reinforcementmember 20 preferably in the form of cords 22, also as previouslydescribed. Longitudinally grooved sheave contact portion 14 is in theform of a plurality of raised areas or apexes 36 alternating with aplurality of trough areas 38 having oppositely facing sides which definedriving surfaces 34 of the belt 32. In each of these instances of FIGS.1-3, sheave contact portion 14 is integral with main body portion 12 andmay be formed from the same elastomeric material to be described ingreater detail below, or layered of different material. While thepresent invention is illustrated with reference to the embodiments shownin FIGS. 1-3, it should be understood that the present invention is notto be limited to these particular embodiments or forms as illustratedbut rather is applicable to any belt construction within the scope ofthe claims as defined below.

Carbon fiber is typically made by carbonizing another fiber such aspolyacrylonitrile fiber, wherein during the carbonizing process thediameter of the fiber is substantially reduced. Carbon yarn is generallycharacterized by the number of fibers contained therein rather than bydenier or dtex. A nomenclature of numbers and the letter “k” are used todenote the number of carbon fibers in a yarn. Of course, carbon fibermay be characterized by such other terms where desired. In a “3k” carbonfiber yarn, the “k” is an abbreviated designation for “1000 fibers,” andthe “3” designates a multiplier. Thus “3k” carbon yarn identifies a yarnof 3000 fibers or filaments. The filaments are generally of sufficientlength to be considered continuous. Like other textile materials, anumber of carbon fibers are combined to form a yarn. A yarn may becombined with other yarn to form a larger yarn, and the yarn or yarnbundles may be twisted together to form a cord. Carbon fiber may have anextremely small diameter which may be in the range of from about 4 toabout 8 microns, or about 5 to 7 microns. Individual fibers are easilyfractured when a yarn is processed to form a cord. For this reason, itis desirable to minimize the number of mechanical operations that theyarn is subject to when forming a cord. For example, twisting severalyarns together to form a yarn bundle and reverse twisting the so pliedyarn bundles to form a cord are mechanical operations that fractureindividual fibers. The number of fractures are lessened by reducing thenumber of twisting operations. To form a desired cord size may includebundling together multiple yarns of smaller filament count, for example,five 3k yarns to obtain 15k (designated 3k-5), or three 6k yarns toobtain 18k cord (designated 6k-3). Preferably the twist level is not toohigh so as not to damage fibers. Thus a preferred twist level is from0.75 to 2.5 turns per inch, or up to about 2 turns per inch. The finalcarbon fiber bundle may be from 3k to 60k, depending on the desiredapplication.

Fiber manufacturers often coat fibers with a sizing which acts tolubricate the fiber and inhibit fracturing as the fiber is processedinto yarns and wound on spools. In some instances, the sizing may have achemical structure that is compatible with an adhesive used to treat acord for inclusion into a power transmission belt. Types of sizing usedby carbon fiber manufacturers include for example epoxies, blends ofepoxy with polyurethane, organosiloxanes, polyamide-imides, and others.Sizing may be present at a pickup weight of about 0.1 to about 2.5%based on the yarn final weight. It is believed that embodiments of theinvention described herein are not particularly sensitive to the type orlevel of sizing which may be present on the carbon fiber. It may be thatthe primary mode of bonding of the PUU adhesive treatment to the carbonfiber bundle is physical interlocking rather than chemical bonding.Also, the present invention may involve using a solvent to apply the PUUadhesive to the carbon fiber bundle, and the solvent may penetrate oreven remove the sizing if desired.

The elastomeric belt (or other article's) body portion may be vulcanizedrubber or other crosslinked elastomer such as cast polyurethane (PU); ormay be thermoplastic elastomer (TPE) or thermoplastic polyurethane(TPU). The PUU cord treatment disclosed herein is particularlycompatible with a cast polyurethane or PUU belt body, and canadvantageously be used therewith without need for any additionaladhesive treatment. Likewise, the PUU cord treatment may be compatiblewith TPE and TPU elastomers and may not require any additional adhesivetreatment for use therewith. In the case of vulcanized rubber articles,it may be advantageous to include one or more additional adhesivetreatments to provide improved bonding between the PUU-treated tensilecord and the vulcanized elastomer. Such an additional adhesive treatmentwill be referred to herein as an overcoat or an overcoat adhesive. Itmay be advantageous to use two different overcoat adhesives to providemaximum bonding between the PUU and a rubber belt body material.

Regarding the main elastomeric body for use with an embodiment of thePUU-treated tensile cord, useful cast PU or PUU compositions that may beutilized in the practice of various embodiments of the presentinvention, and such compositions and methods are described for examplein U.S. Pat. No. 5,231,159 to Patterson et al. and U.S. Pat. No.6,964,626 to Wu et al., the contents of which are incorporated herein byreference. PUU typically has better dynamic properties relative to PUdue to enhanced phase separation, tougher hard segments, etc., and PUUis therefore preferred for high-performance belt applications.

The elastomeric body may be formed of TPE or TPU using for examplethermoplastic lamination processes for long length belting, or suitableother molding processes. TPE types that may be useful in variousembodiments include without limit polystyrene-elastomer blockcopolymers, polyester block copolymers, polyurethane block copolymers,polyamide block copolymers and polypropylene/EP copolymer blends. TPUtypes that may be useful in various embodiments are not particularlylimited, but may include similar chemistry as discussed above inconnection with cast polyurethanes, such as polyester thermoplasticurethanes or polyether thermoplastic urethanes. Thermoplastic beltingembodiments may have the general form of the toothed belt of FIG. 1,e.g. an endless belt, either as molded or by joining two belt endstogether. Embodiments may have two ends which may be clamped to variousassociated mechanisms, for example, in conveying, transporting, holding,or positioning applications.

In each of the cases of FIGS. 1-3 shown above, the main belt bodyportion 12 may be formed of any conventional and/or suitable curedelastomer composition, and may be of the same as or different from thatdescribed below in relation to the optional adhesive rubber membercomprising tensile layer 20. Suitable elastomers that may be utilizedfor this purpose include for example polyurethane elastomers (includingas well polyurethane/urea elastomers and so-called millable gums) (PU),polychloroprene rubber (CR), acrylonitrile butadiene rubber (NBR),hydrogenated NBR (HNBR), styrene-butadiene rubber (SBR), alkylatedchlorosulfonated polyethylene (ACSM), polyepichlorohydrin, polybutadienerubber (BR), natural rubber (NR), and ethylene alpha olefin elastomerssuch as ethylene propylene copolymers (EPM), ethylene propylene dieneterpolymers (EPDM), ethylene octene copolymers (EOM), ethylene butenecopolymers (EBM), ethylene octene terpolymers (EODM); and ethylenebutene terpolymers (EBDM); ethylene vinylacetate elastomers (EVM);ethylene methylacrylate (EAM); and silicone rubber, or a combination ofany two or more of the foregoing.

To form the elastomeric belt (or other article's) body portion 12 inaccordance with an embodiment of the present invention, the elastomer(s)may be blended with conventional rubber compounding ingredientsincluding fillers, plasticizers, stabilizers, vulcanizationagents/curatives and accelerators, in amounts conventionally employed.For example, for use with ethylene-alpha-olefin elastomer and dieneelastomers such as HNBR, one or more metal salts of alpha-beta organicacids may be employed in amounts now conventionally utilized to improvedynamic performance of the resultant article. Thus zinc dimethacrylateand/or zinc diacrylate may be utilized in such compositions in amountsof from about 1 to about 50 phr; or alternatively of from about 5 toabout 30 phr; or of from about 10 to about 25 phr. These materialsfurthermore contribute to the adhesiveness of the composition, andincrease the overall cross-link density of the polymer upon curing withperoxide or related agents through ionic crosslinking, as is now wellknown in the art.

One skilled in the relevant art would readily appreciate any number ofsuitable compositions for utilization in or as the elastomeric portionsof the rubber articles useful herein. A number of suitable elastomercompositions are described for example in The R. T. Vanderbilt RubberHandbook (13^(th) ed., 1996), and with respect to EPM or EPDMcompositions and such compositions having particular high tensilemodulus properties, are furthermore set forth in U.S. Pat. Nos.5,610,217, and 6,616,558 respectively, the contents of which, withrespect to various elastomer compositions that may be suitable for usein the formation of power transmission belt body portions, arespecifically incorporated herein by reference. In an embodiment of thepresent invention associated with automotive accessory driveapplications, the elastomeric belt body portions 12 may be formed of asuitable ethylene alpha olefin composition, such as an EPM, EPDM, EBM orEOM composition.

The elastomeric main belt body portion 12 may moreover be loaded withdiscontinuous fibers as is well known in the art, utilizing materialssuch as including but not limited to cotton, polyester, fiberglass,aramid and nylon, in such forms as staple- or chopped fibers, flock orpulp, in amounts generally employed. In a preferred embodiment relatingto profiled (e.g., as by cutting or grinding) multi-v-ribbed belts, suchfiber loading is preferably formed and arranged such that a substantialportion of the fibers are formed and arranged to lay in a directiongenerally transverse the direction of travel of the belt. In moldedmulti-v-ribbed belts and/or synchronous belts made according to flowthrough methods however, the fiber loading would generally lack the samedegree of orientation.

For use in rubber belts, the PUU-treated cords of the present inventionmay advantageously be coated with a secondary adhesive intended toprimarily coat the outer surface of the cord bundle. Such an adhesive iscalled an overcoat adhesive herein. Overcoat is generally applied at alevel in the range of from about 1% to about 10% dry weight, based onthe final weight of the so treated cord. Examples of useful overcoatadhesives are found in the art and include without limitation variouscompositions sold under the trademarks CHEMLOK or CHEMOSIL by LordCorporation, and various compositions sold under the trademark CILBONDby Chemical Innovations Limited (CIL). The particular overcoat may bechosen to be compatible with both the underlying adhesive treatment andthe rubber belt body and to have other desired properties such as heatresistance, environmental resistance, or the like. It may beadvantageous to apply two separate overcoat adhesive compositions. Ifthe PUU-treated cord is only partially impregnated, a first overcoat maybe used to fully impregnate the cord and a second overcoat to coat theouter surface of the treated cord bundle. For some combinations of PUUtreated cord and a rubber belt body composition, it may be advantageousto use a two-layer overcoat to ensure good bonding, for example, sincePUU may be more polar than many elastomers.

Thus, the invention provides a method for preparing a high-modulustensile cord, such as carbon cord, at least partially filled orimpregnated with a PUU binder. Compared to prior art use of greigecarbon cord (or other high-modulus cords) in cast PU belts, theinvention provides independent control of the cord properties. Forexample, the PUU binder used in a carbon cord may be selected to besofter or harder than the cast PU of the belt body. The invention thusmay result in improved belt handling properties without negativelyimpacting dynamic load or flex capacity. The invention may also improvethe processing and the product produced in low pressure castingoperations and in processes in which the casting resin has a faster geltime or higher viscosity, because the cord is already impregnated with aPUU binder, which give the cord integrity and prevents fraying uponcutting, whether or not the subsequent casting resin penetrates the cordalso. The ability to treat the already-twisted carbon fiber with a lowviscosity adhesive advantageously may produce a generally rounder, moreuniform cord than prior treating methods which required spreading thefibers during treating, followed by twisting.

In one embodiment of a cast PU article or belt having a high modulustooth or body PU compound, the tensile cord may be treated with asolution of polyurethane prepolymer and cured with a smaller curativemolecule or more soft segment or more plasticizer than the cast PU ofthe body, yielding a lower modulus binder of similar, or at leastcompatible chemistry. Thus, the complex modulus of the cord may bereduced (i.e. the flexibility of the cord may be increased) withoutnegatively affecting composite integrity. There is good adhesion betweenthe filled cord and the body/tooth compound. Preferably the body PUcompound is replaced within the cord with a similar prepolymer but witha smaller, more compact hard segment or curative such as water, in orderto give a softer, lower modulus cord treatment. Thus, while the body ofthe article may utilize the same prepolymer but a conventional chainextender such as diamine or polymeric diamine or the like, the cordadhesive curative may preferably include a smaller, more compact diaminecurative and/or additional polyol soft segment and/or plasticizer,resulting in the adhesive being lower modulus than the body.

To apply the PUU adhesive resin to the tensile cord fibers, the adhesivecomposition ingredients may be dissolved or suspended in a suitablesolvent. A suitable solvent is one that will dissolve the prepolymer andalso wet out the fibers of the tensile cord for good impregnation. A lowcontact angle between the solvent or adhesive solution and the fiber isdesirable. Suitable solvents include without limitation, tetrahydrofuran(“THF”), dimethyl sulfoxide, dimethyl formamide, N-methylpyrrolidone(“NMP”), toluene, xylene, benzene, acetone, methyl ethyl ketone, methylisobutyl ketone, and the like. For treating carbon fiber cords accordingto an embodiment of the invention, preferable solvents include THF andtoluene.

In a preferred embodiment, a low free PPDI/polycaprolactone prepolymeris dissolved in a solvent, such as toluene or THF, at a predeterminedconcentration which may be in the range 10-50% by weight, or from 20% to40% by weight, and the solution is added to a dip tank. The cord, whichmay preferably be in twisted form, e.g. from 0.75 to 2.5 turns per inchfor carbon fiber cord, is pulled though the dip tank and then through anoven, where, the solvent is flashed off. Alternately, the cord may bedipped and dried in untwisted form, with means to spread the fibers formaximum penetration, followed by twisting. After passing through theoven, and removing most of the solvent, the prepolymer is allowed toreact with water. If diamine cure is not to be used, the cord can bedipped in a water bath to enhance the reaction before spooling, forexample to prevent sticking of the cord on the spool. The water bathcan, but need not, contain a chemical, such as a catalyst, thataccelerates the formation of a urea skin on the outside of the cord.Likewise heat, for example in a drying oven, can be used to accelerateurea skin formation. The prepolymer on the inside of the cord will curewith ambient environmental moisture. This cure on the inside of the cordmay take several days, but the cord may be used in a product made withcast PU at any time after treating, whether fully cured or not. The cordwill continue to cure as the product is cured. Even a fully cured cordtreatment will generally have sufficient reactive groups to continue tocure and bond with the body material of a product during product cure.Water performs the function of curative by reacting with isocyanategroups on the prepolymer. Isocyanate reacts with water to form carbamicacid. Carbamic acid dissociates to form an amine and carbon dioxide. Theamine will react with another isocyanate to form a di-substituted urealinkage and further the condensation reaction. This reaction creates avery compact hard segment with urea linkages.

If a commercially available blocked prepolymer is used with aminecurative, the process may be essentially the same as described above,except the result will be a faster drying/curing treatment, with lesssticking of cord to itself on a reel. Because of the faster reactiontime using diamine curatives with blocked prepolymer (compared to watercure), the dip process may need to be adjusted to obtain betterpenetration of the cord by the dip, for example, by running the dip lineat a different speed or tension, or with different residence time in thedip solution.

Alternately, when blocking is done in situ, i.e., while making up theadhesive solution, the process may be suitably altered somewhat. If anunblocked prepolymer is to be blocked, for example with MEKO or DMP, theprocess may be modified as followed. The prepolymer and the blockingagent may be reacted in a solvent solution, using one of the suitablesolvents describe above. A slight excess of blocking agent may be usedto ensure complete blocking of all isocyanate groups. For example, a1.05 molar ratio of blocking agent to NCO may be used. In one exemplarycase, the reaction was completed in eight hours at room temperature in adrum with stirring, but other reaction conditions could be used. Heatmay be used to speed up the blocking reaction. To the resulting blockedprepolymer solution may be added the diamine, triamine, and/ortetramine, and optionally a polyol, such as a diol or triol or mixturethereof, and/or plasticizer or other ingredients. The resulting dipsolution may be used to treat a tensile cord by dipping, spraying, etc.Upon drying the cord at a suitably high temperature and residence time,the solvent may be driven off, the blocking agent released(“de-blocked”), and the polyurethane-urea reaction product formed by thereaction between the de-blocked isocyanate-terminated prepolymer, thepolyamine(s) and the optional polyol. A blocked prepolymer may utilize acatalyst to make it de-block faster.

The advantages of the blocking approach are many. The dip solutions arerelatively stable and have good shelf life. The blocked-prepolymerapproach is the most stable and versatile, since the blocked prepolymeris more stable to heat and moisture and to other ingredients likepolyols. Once de-blocked, the reactions proceed very quickly, resultingin faster processing and a drier cord which does not stick to itself.The formulation options are many, so that the treatment can be madesofter or harder than the belt body formulation, as desired. Althoughmuch of the blocking agent may be driven off in the drying/curing step,traces of blocking agent may remain in the treated cord and/or the finalproduct, thus distinguishing the cord or product from non-blockedalternatives.

According to an embodiment of the invention, the PUU treatment mayadvantageously be 20-40% solids and preferably of low enough viscosityto fully penetrate the fiber bundle during a dip treatment whethertwisted or not. After the solvent is removed by drying (possibly alongwith curing or partial curing), the PUU preferably coats the individualfibers of the bundle, but need not completely fill the interstices ofthe cord. It may be advantageous for the PUU resin to occupy from about20% to about 99% or 100% of the interstices, depending on the intendeduse of the treated cord. In particular, for use in cast polyurethanearticles such as power transmission belts, only partially filling theinterstices, e.g., from 20% to 90%, or 30% to 80% full, or 40% to 60%full, may leave interstices or voids that can be penetrated by the castPU of the belt body, thus providing a level of mechanical adhesionwithout making the cord overly stiff and still benefitting from the useof the PUU treatment. When a cast PU belt body thus penetrates voids inthe PUU-treated cord, the PU and PUU materials may be in intimatecontact, facilitating chemical bonding between them. On the other hand,when the cord is to be overcoated with additional adhesives for chemicaladhesion as might be done for bonding in certain rubber articles, morefully impregnated cord may be more suitable, e.g., from 40% to 100%, or60% to 99% full. The pickup levels, indicated for example as weight %adhesive pickup based on weight of the greige (untreated) cord, may varydepending on the degree of voids or interstices in the twisted cord. Thepick up level of the PUU adhesive on the cord may be in the range from6% to 25%, or 8% to 22% or from 10% to 20%.

Cast urethane belts according to an embodiment utilizing the inventivetensile cords may be made according to known methods such as thosedescribed in references already incorporated herein by reference.Likewise, TPE or TPU belts may be made by known methods, includingcontinuous lamination/extrusion methods that produce belts having twoends, instead of endless belts. The two ends may be joined according toknown methods to make endless TPE or TPU belts. Rubber belts may bebuilt on a mandrel, cured, and cut to width according to methods knownin the art.

It should be understood that reinforcing cords according to anembodiment of the invention may be used in various kinds of elastomericcomposite articles, such as power transmission belts, transport ortransfer belts, conveyor belts, straps, tires, hose, air springs,vibration mounts, etc.

Examples

The following illustrations and examples are not meant to limit theinvention, but demonstrate its usefulness in various embodiments.Examples demonstrate use of the invention in cast polyurea-urethane beltapplications, TPU belt applications, and rubber belt applications.

Illustration I.

A pair of 12k-1 yarns from Toho were twisted in opposite directions to alevel of 2.0±0.1 turns per inch to form “S” and “Z” 12k carbon cords. Aportion of the greige, twisted cord was used to make a slab of cast PUtoothed belts of 8-mm pitch according to the method of U.S. Pat. No.5,807,194 to Knutson et al., referred to herein as Comparative Example 1(“Comp. Ex.” 1). Another portion of the cord was treated according to anembodiment of the present invention and then used to make a second slabof inventive 8-mm-pitch, toothed belts, referred to herein as Example 2(“Ex.” 2).

For the PUU adhesive treatment of Ex. 2, a blend of di- andtri-functional PPDI-terminated polycaprolactone prepolymer with a finalfunctionality of approximately 2.1 was added to toluene solvent to makea 33 weight-percent solids solution for the dip tank. The greige twistedcord was dipped and then the solvent flashed off by passing the wet cordthrough an oven. Immediately after exit from the oven the cord wasdipped in a water bath, air dried, and then wound onto a spool. Solidspickup was determined for “S” and “Z” dipped cords at 16.1 and 14.0weight percent, respectively. Cord stiffness was measured immediatelyafter spooling and after sitting in a high humidity environmentovernight. Cord stiffness was measured on a Tinius Olsen StiffnessTester according to the procedure of ASTM D747 but based on the actualpeak bending force in units of pounds force (or kilograms force) forfive parallel cords tested at a 12.7-mm span over a deflection range offrom zero to 65°. The initial stiffness of Ex. 2 was 0.49 and 0.73 lbf,respectively. After sitting overnight the stiffness was measured at 1.14and 1.08 lbf, respectively. Water cure may be relatively slow, resultingin a gradual change in stiffness over hours or even days. Based on thereported equivalent cross section of carbon in the yarn (0.00455 cm²)and the final cord cross sectional area in the belts (0.00665 cm²), thevoid volume in the cord was calculated to be about 31.6% of the finalcross section. The weight percent of treatment picked up for the S and Zcords thus corresponds to the interstices of the cord being filled about55 to 60 percent with PUU resin. Inspection of the resulting cordsshowed that the outer layer of fibers was lightly coated leaving plentyof interstitial space for additional impregnation by the cast PU duringbelt building, resulting in very good adhesion of the cord to the beltbody. Tensile testing of the treated cord versus the greige cord yieldeda tensile strength of 148 lbs for the greige cord and 222 lbs for thetreated cord, a 50% improvement. This dramatic improvement in tensilestrength may reflect the difficulties in tensile testing greige yarns,and the improvement in handling properties of the treated yarn.Inspection of belt cross sections under high magnification revealed thatthe cast PU resin had substantially fully filled all intersticesremaining after adhesive treating the cord. The cast PU resinformulation used to make the belts was based on a TDI-terminatedpolyether prepolymer based on polytetramethylene ether glycol (“PTMEG”),cured with TMGDAB.

After belt manufacture, samples of cord were removed from greige- andtreated-cord belts and subjected to the cord stiffness test. Twoparallel cord samples were used instead of the usual five. The cord fromComp. Ex. 1 was stiffer than the treated cord, from Ex. 2, namely 0.66vs 0.52 lbf, respectively. The inventive cord treatment thus lowered thestatic bending stiffness of the cord in the belt by approximately 20%.

Dynamic belt bending testing at two frequencies and temperatures alsoshowed a significant modulus difference between greige and treatedcords. The results for this testing are presented in Table 1. At alltest conditions, belt bending moduli were lower for the belt withtreated cord of Ex. 2 than for the belt with greige cord of Comp. Ex. 1.Treatment of the cord with the inventive PUU adhesive treatment reducedthe dynamic bending modulus of the cord.

TABLE 1 Comp. Ratio of Ex. 2: 3-point dynamic bending test Ex. 1 Ex. 2Comp. Ex. 1 K* at 23° C., 0.1 Hz (N/mm)¹ 7.86 5.00 0.64 K′ at 23° C.,0.1 Hz (N/mm)² 7.59 4.88 0.64 K″ at 23° C., 0.1 Hz (N/mm)³ 2.03 1.090.53 K* at 100° C., 0.1 Hz (N/mm) 5.96 3.65 0.61 K′ at 100° C., 0.1 Hz(N/mm) 5.87 3.62 0.62 K″ at 100° C., 0.1 Hz (N/mm) 1.02 0.49 0.48 K* at23° C., 1.0 Hz (N/mm) 8.40 5.14 0.61 K′ at 23° C., 1.0 Hz (N/mm) 8.135.05 0.62 K″ at 23° C., 1.0 Hz (N/mm) 2.12 0.97 0.46 K* at 100° C., 1.0Hz (N/mm) 5.91 3.71 0.63 K′ at 100° C., 1.0 Hz (N/mm) 5.84 3.68 0.63 K″at 100° C., 1.0 Hz (N/mm) 0.93 0.46 0.49 ¹K* is the complex stiffness.²K′ is the storage or elastic stiffness. ³K″ is the loss or inelasticstiffness.

The PUU treatment of Ex. 2 was also mixed into THF at a concentration of25% solids by weight and used to cast a film on an IR window. Theresulting PUU film was 0.018 inches thick. It was placed in FTIRinstrument to follow the solvent evaporation and the reaction of the NCOgroups with water. The NCO peak area was reduced 50% after about 200minutes, and substantially gone after about 500 minutes. An attempt wasmade to cast a thicker film of the inventive treatment and the cast PUUof the belt body for tensile testing. Though some bubbles were observed,the resulting films were deemed sufficient for a tensile testcomparison. The water-cured adhesive treatment exhibited a modulus about⅔ less than that of the TMGDAB-cured belt material, an elongation aboutthe same, and a tensile strength about ⅓ less. Thus, according to anembodiment of the invention, a reinforcing cord may be treated with amoisture-cured PUU analog of a diamine-cured PUU casting composition toobtain a relatively lower modulus, more flexible cord with equivalent tomuch better tensile strength, and with excellent compatibility with thecast PUU.

The belts of Ex. 2 were subjected to a number of tests, demonstratingcertain advantages over Comp. Ex. 1. Belt tensile strength was measuredby mounting a belt on two 60-groove sprockets, and pulling on aconventional tensile test machine at 25.4 mm/min with a clip-onextensometer optional. Flex Conditioning of the belts was carried out ona two-point layout with two 22-groove pulleys driven at 3600 rpm with165-pound deadweight tension for 168 and 336 hours. Retained tensilestrength after (i.e., “post”) flex conditioning is reported in Table 2.In a back-bending test, belts were back-bent three times in the samelocation of the belt around a pipe of given diameter and then tensiletested with the damage location in the span between the two pulleys. Theretained tensile strength after back bending is also reported in Table2. Static cord adhesion tests (pulling a short length of two cords outof the belt) and a static tooth shear test on the belts showed nosignificant differences between Comp. Ex. 2 and Ex. 1. Finally, dynamicbelt tests were run on a dynamometer rig (“Dyno Testing”) to evaluatebelt load capacity, dynamic adhesion, durability and the like. DynoTesting used an 18-mm wide, 140-tooth, 8-mm GT® profile belt run at 19hp and 2000 rpm, on two 24-groove pulleys with 213 pounds dead weighttension at room temperature. Two different testers known forsignificantly different results were used. Two belt lives were averagedfor each result reported in Table 2.

It can be seen from Table 2 that the inventive belt has slightly highertensile strength initially and after flex conditioning than the controlbelt. This may be attributable to the treated cord having improvedhandling tolerance over the greige cord. However, the back-bending testshows most clearly a dramatic advantage of the softer PUU-treated cordover the greige cord. While the greige cord loses half its strengthafter the 27-mm back bends, the inventive cord suffers no strength loss.At tighter back bends, the inventive cord does lose strength, but at amuch lesser rate than the control belt. Thus, the inventive beltperforms similarly under 10-mm bends as the control under 27-mm bends.It can also be seen from Table 2 that the Ex. 2 belts performed a littlebetter on average than the control belts on the Dyno Testing (the toothshear failure mode was observed for all belts). Thus, the soft PUUadhesive treatment provides significant improvement in handlingtolerance without loss of other performance features such as adhesion orload capacity.

TABLE 2 Belt Tensile Strength Tests Comp. (lbf/inch belt width) Ex. 1Ex. 2 Initial Tensile Strength 9406 11552 Post Flex Conditioning (168hrs.) 9500 10000 Post Flex Conditioning (336 hrs.) 9400 10000 After backbends at 27-mm diameter 4800 10900 After back bends at 17-mm diameter2600 7000 After back bends at 10-mm diameter 2000 4600 After back bendsat 4.5-mm diameter 1700 3700 Dyno Testing On Tester #1 (average life inhours) 316 379 On Tester #2 (average life in hours) 43.4 68.4

Illustration II.

In a second test series, belt Comp. Ex. 3 and Ex. 4 were constructedwith a polyester-based TPU belt body and woven nylon fabric on the toothsurface. These toothed belts were endless with a metric T10 profile (10mm pitch, and trapezoidal tooth shape) and cut to a width of 25 mm.Comp. Ex. 3 was constructed with a conventional steel cord, and Ex. 4used the same inventive cord of Ex. 2 above. Specimens of these twobelts were subjected to a cord adhesion test, the results of which areshown in Table 3. Table 3 shows that the inventive treated cord in Ex. 4has equal or better adhesive performance than the conventional cord usedin Comp. Ex. 3, demonstrating that an embodiment of the invention issuitable for use in TPU belts.

TABLE 3 Comp. Ex. 3 Ex. 4 Cord adhesion (N) 977.1 1060.4 Failure modeCord Adhesive break

Illustration III.

For this series, Torayca 12k-1 yarns were used to make 8-mm pitchtoothed, cast PUU belts as in Illustration I. Control belts made withgreige, twisted cord are referred to as Comp. Ex. 5. A portion of thecord was treated according to another embodiment of the presentinvention and then used to make a slab of inventive 8-mm pitch toothedbelts, referred to herein as Ex. 6. The PUU adhesive treatment of Ex. 6comprised a polyester/TDI prepolymer, with a MEKO blocking agent on theisocyanate groups. The curative was the diamine, DETDA. The liquidmixture of blocked prepolymer and curative was impregnated into thecarbon fiber bundle under pressure, though use of a solvent as describedabove would have been easier. The belts were again evaluated for tensiledecay on the Flex Conditioning test, but at 150 pounds dead weighttension, and for handling damage by both back-bending and forwardbending on pipes of various diameters. The results are shown in Table 4.It can be seen that this embodiment also exhibits improved handlingresistance over the control. In another example of using a blockedprepolymer, designated Ex. 7, the curative was the diamine, MCDEA, butno belt data is available.

TABLE 4 Belt Tensile Strength Tests Comp. (lbf/inch belt width) Ex. 5Ex. 6 Initial Tensile Strength 12100 10100 Post Flex Conditioning (2hrs.) 8800 10100 Post Flex Conditioning (24 hrs.) 8600 10200 Post FlexConditioning (48 hrs.) 8000 10200 Post Flex Conditioning (190 hrs.) 80009900 After back bends at 50-mm diameter 5800 10300 After front bends at37-mm diameter 5500 10600

Illustration IV.

In this set of examples, an embodiment using PUU-treated carbon cord iscompared to a conventional RFL-treated carbon cord in a rubber, toothedbelt. A 12k-1 carbon bundle was again PUU treated as in Ex. 2 ofIllustration I, but in addition, the treated cord was dipped in aCilbond 81 overcoat adhesive and dried again. For a control, anX—HNBR-RFL treated 12k cord was prepared according to the methods ofU.S. Pat. No. 6,695,733 (see Table 1 therein and associated text, whichis hereby incorporated herein by reference), and also overcoated withCilbond 81. Toothed belts were made according to well-known methods,including applying a nylon fabric sleeve to a 97-groove (9.525-mm pitch)mandrel, helically winding both S and Z twisted cords at 18 totalstrands per inch giving suitable spacing to allow rubber to flowthrough, applying a layer of sulfur-cured HNBR rubber, and curing underpressure and temperature so that the rubber flows through the cord,presses the fabric into the grooves and forms the teeth, as thecomposite is cured. After removal of the resulting sleeve from themandrel, individual belts were cut to 19 mm width. The control beltswith RFL-treated cord are designated Comp. Ex. 8, and the inventivebelts with PUU-treated cord are designated Ex. 9. A number of belt testswere conducted and the results are shown in Table 5. The tensilestrength was measured as previously described, as was cord adhesion. Thejacket adhesion test involved peeling the tooth fabric off the belt,giving a minimum in the web region where jacket-cord adhesion isprimarily measured and a maximum in the tooth region where jacket-rubberadhesion is primarily measured. The belt running temperature wasmeasured over a 24 hour period on a no-load Flex Test rig. The Flex Testis illustrated in FIG. 4. A 97-tooth synchronous belt was run on adriving pulley 50 with 19 grooves, two driven pulleys 52 and 54, with 19grooves and 20 grooves respectively, two backside idlers 56 (50-mmdiameter) and a tensioner 58. A tension of 200 N was applied withtensioner 58 by a hanging weight. The Flex Test ran at 6200 rpm at roomtemperature.

Table 5 shows that the rubber belts according to the invention performcomparably to the control belts. It was noted that in some cases, theoriginal inventive belts tested inferior to the control, while the airaged inventive belts were comparable, e.g., on the cord adhesion testand the dynamic tooth durability test. This is believed due to the slowcure of the PUU material and indicates a possible advantageous use of apost-cure treatment or addition of a catalyst to the adhesive or anamine-based cured, for some embodiments of the invention. On the FlexTest rig, the inventive PUU-treated cord resulted in lower belt runningtemperatures than RFL-treated cord, which is believed attributable toimproved dynamic properties of PUU over RFL.

TABLE 5 Comp. Ex. 8 Ex. 9 Original Air Aged Original Air Aged TensileStrength 43 44.5 31.5 32.5 (kN/20 mm) Cord Adhesion (N) 1050 1200 6501050 Jacket-Cord (Web) 28 26 26.5 25 Adhesion (N) Jacket-Tooth Adhesion140 110 100 110 (N) Belt Running 112 108 — 102 Temperature (° C.)Dynamic tooth 3000 10000 300 100,000 durability (cycles)

Illustration V.

This series of examples is largely a repeat of Illustration I, but with27.5% solids in the adhesive solution, variations in adhesive pickuplevels, and with a variety of other carbon cord sizes, including a muchlarger, 12k-4 carbon cord bundle twisted 1.2-1.3 turns per inch. Amoisture cure without water dip after treatment was used. As before, aportion of the greige, twisted cords (both S and Z) were used to makecomparative cast-PUU, toothed belts according to the method of U.S. Pat.No. 5,807,194 to Knutson et al. As indicated in Table 6, the treated12k-4 carbon cords (made from the Toho 12k yarns of Illustration I) weremade into 14-mm-pitch HTD®-profile belts. The 14-mm belts of thisillustration utilized the same cast PUU resin formulation for the beltbody as in Illustration I above, i.e., a TDI-terminated polyetherprepolymer based on PTMEG, cured with TMGDAB. As shown in Table 6, the12k-4 cords of Ex. 11 and 12 showed improved tensile strength over thegreige cords of Comp. Ex. 10. The increase in stiffness relative to the12k-1 cords of Illustration I is commensurate with the increased corddiameter. The increase in tensile strength of the cords after treatmentis comparable to that observed above in Illustration I. The dip pickupsranged from 10.3 to 14% for this run of 12k-4 cord. Finally, note thatthe handling testing for the belts of Ex. 11 and 12 again shows dramaticimprovements in tensile strength retained after back bending overpulleys of decreasing size, relative to the Comp. Ex. 10.

TABLE 6 Comp. Ex. 10 Ex. 11 Ex. 12 Carbon Cord 12k-4 12k-4 ConstructionSolids Pick Up (S,Z) — 11, 12.8 (%) Tensile Strength (avg.) 530 926 (lb)Stiffness (S,Z) (lbf, — 6.17, 6.22 after 23 d) Belt Tensile StrengthTests (14-mm HTD) Made in (lbf/inch belt width) Cell 3 Cell 3 Cell 1Initial Tensile Strength 21308 20469 17657 (inverted on 102-mm diameterpulleys) After back bends at 43-mm 11441 16526 16763 diameter After backbends at 33-mm 8159 13930 15284 diameter After back bends at 28-mm 573511632 14480 diameter

The results shown in Table 7 indicate that the invention is applicableto making a range of cord sizes, in this illustration from 12k-1 to18k-1. The results of Table 7 also show a wide range of solids pickupvalues for the resulting cords, from 6.2% to 17%. In each case, theinventive example cord shows significant improvements in tensilestrength over the greige cord, which is most likely indicative ofimproved handling in the tensile test. It is also noteworthy that thetensile strength of the inventive cords was independent of the solidspickup level, so a single average value is reported for both S and Zcords. Cord stiffness appears to increase with cord size and with solidspickup.

Microscopy was performed on various of the cord examples as prepared andon belt cross sections after casting or forming. The outside of theinventive cord is generally free of a polymeric skin. The outer fibersof the cord generally appear to be well coated with PUU, but notnecessarily bound together, but neither are the outer fibers likely tofly away or fray upon cutting the cord. The inside of the cord isgenerally very well penetrated with PUU adhesive, but not necessarilytotally filled. The belt body material in the cast urethane belts isgenerally able to penetrate the treated cord and almost completely fillthe remaining interstices. This is believed to provide excellentphysical or mechanical adhesion, as well as chemical adhesion. Dependingon treatment conditions, the treated cord may not be as circular incross section as the greige cord due to the drying and polymerization orcuring of the treated cord on a spool. Thus, the invention cord may haveflats formed where it sits upon previous layers of cord due to windingon a spool.

TABLE 7 Comp. Comp. Ex. Ex. Ex. Ex. Comp. Ex. Comp. Ex. 13 14 15 16 Ex.17 18 Ex. 19 20 Carbon Cord Toho Toho Grafil Grafil Grafil Grafil GrafilGrafil Construction 12k-1 12k-1 12k-1 12k-1 15k-1 15k-1 18k-1 18k-1Solids Pick Up (S, Z) — 6.2, — 8.8, — 7.8, — 6.2, (%) 17 12 14.9 15.7Tensile Strength (avg.) 157 281 149 274 216 329 230 380 (lb) Stiffness(S, Z) (lbf, — 0.77, — 0.91, — 1.09, — 1.1, after 23 days) 1.27 1.071.64 1.77

Illustration VI.

In this series of examples, blocked isocyanate-terminated prepolymerswere used as in Illustration III above, but using solvent solutions toapply the adhesive composition to the carbon fiber tensile cords. Inaddition, polyols were used to optimize the cured adhesive modulus tobelow that of the cast urethane matrix used for the body of 11-mm HTD®belts. The resulting belts were tested for back bend resistance in thesame way as in Illustration I above, i.e., retained tensile strengthafter 3 back-bends over the indicated diameter of rod. Also, dynamicbelt tests were run on a dynamometer rig (“Load Life Testing”) toevaluate belt load capacity, dynamic adhesion, durability and the like.Load Life Testing used an 10-mm wide, 108-, 111-, or 113-tooth, 11-mmHTD®-profile belt run at 15 hp and 1750 rpm, on two 30-groove pulleyswith 396 pounds total dead weight tension and a 5/1 tension ratio atroom temperature. Two different testers known for generating comparableresults were used. Two belt lives were averaged for each result reportedin Table 8. The lives could have been normalized based on number ofcycles for the different lengths tested, but the small difference (<5%)was not considered significant for these illustrations.

The belt test results are presented in Table 8. The control belt had noadhesive treatment on the carbon fiber tensile cord, but had goodpenetration from the cast PU belt body. Ex. 2′ was made like Ex. 2above, but with the 11-mm HTD® profile. Ex. 21 and 22 were DMP-blockedPPDI-polycaprolactone prepolymers with added polycaprolactone triol. Ex.23 was a DMP-blocked TDI-polyether prepolymer with addedpolycaprolactone triol. The blocking in Ex. 21-23 was done in theprocess of making the adhesive solution (i.e., in-situ). Ex. 24 was acommercial, DMP-blocked, TDI-polyether prepolymer, and polycaprolactonediol was also added to the adhesive composition. All four examples usedMDEA as the curative. It is clear the inventive examples retain tensilestrength much better than the control belt. In addition, the use of theblocked prepolymer with polyamine cure gives a significant improvementin back-bend resistance over the moisture cured approach. Moreover, theLoad Life Test result is improved even though the adhesive treatment issofter than the belt body material. In some cases, (namely Ex. 21 and23) the load life is about triple that of the control. In contrast, theDyno Test results for Illustration I (water cure) showed more modestimprovement over the control, and the durability results in IllustrationIV only suggested improvement after a long post-cure. The back bendtensile data of Table 8 are also plotted in the graph of FIG. 5.

TABLE 8 Belt Tensile Strength Tests (lbf/inch belt width) Control Ex. 2′Ex. 21 Ex. 22 Ex. 23 Ex. 24 Initial Tensile Strength 10210 10948 1135911689 11005 10992 After back bends at 1-in diameter 5374 8145 1025511218 10564 9965 After back bends at ¾-in diameter 4258 5927 10186 1160610664 9023 After back bends at ½-in diameter 3338 4135 9437 10436 97288812 After back bends at ¼-in diameter 2545 2893 7848 7852 8220 6373Load Life Testing (hours) 85 — 250 127 255 118

To further compare the improvement in Load Life of these belts over themoisture cure method, a series of 8 belts each from Ex. 2′ and Ex. 21were tested on the Load Life Test. This provided sufficient repeats fora Weibull distribution analysis of the data. The Ex. 21 belts had livesof 210, 220, 230, 240, 260, 270, 300, and 400, resulting in a WeibullEta and Beta of 291 hours and 6.4, respectively, while the Ex. 2 beltshad lives of 105, 110, 110, 130, 190, 220, 310, and 400, resulting in aWeibull Eta and Beta of 221 hours and 2.4, respectively. (Eta isindicative of an average life, and Beta is indicative of the narrownessof the distribution.) Thus, the Ex. 21 belts have about ⅓ longer life onaverage, but also much narrower distribution in belt life, reflectingmuch fewer shorter-life results. While five out of eight of the Ex. 2belts had lives between 100 and 200 hours, none of the Ex. 21 belts hada life below 200 hours. FIG. 6 is a Weibull plot of these two examples,Ex. 2′ and Ex. 21.

Crimp resistance is one of the key benefits from exemplary belts. Tofurther demonstrate this, both crimp resistance and Load Life Testingwere combined. For this particular test, belts from Ex. 2′ and Ex. 21were back bended at 0.25″ diameter three times and then subjected toLoad Life Testing. The belts of Ex. 21 failed normally, i.e., withsimilar lives and failure modes as the not-crimped, control belts.However, crimped belts of Ex 2′ failed within minutes by tensile breakat the bend location.

Illustration VII.

This series was carried out in a similar way to the previous series,Illustration VI, but the blocking agent used was MEKO. Ex. 25 uses aMEKO-blocked prepolymer based on TDI/poly(tetramethylene ether) glycoland Ex. 26 uses a MEKO-blocked prepolymer based on PPDI/polycaprolactonediol. Both used MCDEA as the curative and include additionalpolycaprolactone diol. It is clear the inventive examples retain tensilestrength much better than the control belt. In addition, the use of theblocked prepolymer with polyamine cure gives a significant improvementin back-bend resistance over the moisture cured approach of Ex. 2′.Moreover, surprisingly, the load life is improved even though theadhesive treatment is softer than the belt body material. The back bendtensile data of Table 9 are also plotted in the graph of FIG. 7.

TABLE 9 Belt Tensile Strength Tests (lbf/inch belt width) Control Ex. 2′Ex. 25 Ex. 26 Initial Tensile Strength 10210 10948 10588 9941 After backbends at 1-in diameter 5374 8145 10206 — After back bends at ¾-indiameter 4258 5927 9310 9345 After back bends at ½-in diameter 3338 41357754 8505 After back bends at ¼-in diameter 2545 2893 6285 — Load LifeTesting (hours) 85 — 164 230

Illustration VIII.

In this series of examples, isocyanate-terminated prepolymers were usedwith blocked amine curatives and optionally a plasticizer to adjust thecured adhesive modulus. The prepolymer was PPDI/polycaprolactone in Ex.27 and TDI/polytretramethylene glycol in Ex. 28 and Ex. 29. The blockedamine was tris(4,4′-methylene dianiline) sodium chloride dispersed indioctyl adipate. The plasticizer was a blend of C6, C8 and C10phthalates, and the amount was 80% by weight of the prepolymer in Ex. 27and Ex. 29, and no plasticizer was used in Ex. 28. The molar ratio ofamine functionality to NCO functionality was 90%. The solids content ofthe adhesive composition was 40% by weight. The adhesive composition wasapplied to the carbon fiber tensile cords as before. Belts and testingwere analogous to Illustration VI above, with the same control belt. Thebelt test results are presented in Table 10. It is clear the inventiveexamples again retain tensile strength much better than the control beltwhen mishandled by back bending. In addition, the use of the blockedpolyamine cure gives a significant improvement in back-bend resistanceover the moisture cured approach of Ex. 2′. The back bend tensile dataof Table 10 are also plotted in the graph of FIG. 8. Moreover, the loadlife is significantly improved when plasticizer is used, even though theadhesive treatment is softer than the belt body material. However, itshould be noted that when no plasticizer is used, the back-bendingresistance is still excellent even though the load life drops to aboutthat of the control. This seems to contradict conventional wisdom thatteaches that higher modulus adhesive will carry high belt loads, but beless flexible. The evidence seems to show that simply using the blockingprocess described herein can simultaneously improve both back bend (orcrimp) resistance and load life in a belt.

TABLE 10 Belt Tensile Strength Tests (lbf/inch belt width) Control Ex.2′ Ex. 27 Ex. 28 Ex. 29 Initial Tensile Strength 10210 10948 9783 101959767 After back bends at 1-in diameter 5374 8145 9504 10174 9037 Afterback bends at ¾-in diameter 4258 5927 8868 8641 8588 After back bends at½-in diameter 3338 4135 7807 8093 7460 After back bends at ¼-in diameter2545 2893 6819 6568 6590 Load Life Testing (hours) 85 — 339 76 196

In other exemplary experiments involving casting polyurea films forphysical property testing, a variety of suitable adhesive compositionswere obtained using various blocking agents, variousisocyanate-terminated prepolymers, various amine curatives, and variouspolyols and/or plasticizers, and at various ratios or levels. Theinvention was thus determined to be broadly practical as defined hereinand in the claims. Some of these film experiments are listed in Table11, with Shore A hardness, tensile strength, and elongation as thephysical properties. Ex. 21 and Ex. 25 mentioned above are included forcomparison. Ex. 30 and Ex. 31 are similar to Ex. 25 but with CAP or DMPrespectively as the blocking agent and no additional polyol. Likewise,Ex. 32 is similar to Ex. 21, but with no additional polyol. Ex. 33 usesMDI instead of PPDI. Ex. 34 thru 37 show the use of different levels ofplasticizer to adjust hardness instead of polyol in a formulationsimilar to Ex. 21.

TABLE 11 Cast Film Formulation and Properties Ex. 21 Ex. 25 Ex. 30 Ex.31 Ex. 32 Ex. 33 Prepolymer-isocyanate PPDI TDI TDI TDI PPDI MDIPrepolymer-polyol PCL PTMEG PTMEG PTMEG PCL PCL Blocking agent DMP MEKOCAP DMP DMP DMP Polyamine MDEA MCDEA MDEA MDEA MDEA MDEA Polyol PCLtriol PCL diol — — — — Plasticizer¹ (parts/100 — — — — — — prepolymer)Hardness (Shore A) 81 82 83 84 91 89 Tensile Strength (psi) 2790 18511867 4844 8491 6544 Elongation at Break (%) 315 361 361 640 409 372 CastFilm Formulation and Properties Ex. 34 Ex. 35 Ex. 36 Ex. 37Prepolymer-isocyanate PPDI PPDI PPDI PPDI Prepolymer-polyol PCL PCL PCLPCL Blocking agent DMP DMP DMP DMP Polyamine MDEA MDEA MDEA MDEA Polyol— — — — Plasticizer¹ (parts/100 40 50 60 70 prepolymer) Hardness (ShoreA) 85 82 81 79 Tensile Strength (psi) 4131 3560 2232 1769 Elongation atBreak (%) 503 541 418 421 ¹PEG di-2-ethylhexoate

TABLE 12 includes examples that demonstrate the embodiment wherein theadhesive composition is based on a blocked polyisocyanate with a polyol,instead of a blocked prepolymer. Ex. 38 and 39 have a DEM-blocked blendof HDI and IPDI, with a PCL triol in Ex. 38 and a PCL tetraol in Ex. 39.These actually form urethane polymers. Ex. 40 thru 42 have aMEKO-blocked polymeric MDI with added PCL polyol and MDEA polyamine. Ex.42 has a higher ratio of triol relative to the blocked isocyanate thanEx. 41.

TABLE 12 Cast Film Formulation and Properties Ex. 38 Ex. 39 Ex. 40 Ex.41 Ex. 42 Blocked-isocyanate HDI/IPDI HDI/IPDI MDI² MDI² MDI² Blockingagent DEM DEM MEKO MEKO MEKO Polyol PCL triol PCL tetraol PCL diol PCLtriol PCL triol Polyamine — — MDEA MDEA MDEA Hardness (Shore A) 32 63 5265 75 Tensile Strength (psi) 225 461 582 596 817 Elongation at Break (%)160 71 364 151 152 ²polymeric MDI blend with about 60% MDI.

Embodiments of the invention exhibit a number of advantages over theprior art. The invention can eliminate cord fraying during cutting andprovide improvements in belt tensile strength, belt bending endurance,and resistance to handling damage. Generally, other physical propertiesof the belt, related to belt performance, have not been negativelyimpacted by the invention. For example, in the case of cast PU belts,flex fatigue resistance and load life capacity of belts of the inventioncan be much better than belts produced from greige cord. Similaradvantages should be realizable in other reinforced elastomerapplications such as those listed and/or illustrated previously herein.

Although the present invention and its advantages have been described indetail, it should be understood that various changes, substitutions, andalterations can be made herein without departing from the scope of theinvention as defined by the appended claims. Moreover, the scope of thepresent application is not intended to be limited to the particularembodiments of the process, machine, manufacture, composition of matter,means, methods, and steps described in the specification. As one ofordinary skill in the art will readily appreciate from the disclosure ofthe present invention, processes, machines, manufacture, compositions ofmatter, means, methods, or steps, presently existing or later to bedeveloped that perform substantially the same function or achievesubstantially the same result as the corresponding embodiments describedherein may be utilized according to the present invention. Accordingly,the appended claims are intended to include within their scope suchprocesses, machines, manufacture, compositions of matter, means,methods, or steps. The invention disclosed herein may suitably bepracticed in the absence of any element that is not specificallydisclosed herein.

What is claimed is:
 1. A belt comprising: an elastomeric body, and atensile cord embedded in the elastomeric body; with the tensile cordimpregnated with an adhesive composition comprising the reaction productof: a polyisocyanate and a first polyol or a polyurethane prepolymercomprising said polyisocyanate and said first polyol; and at least onecurative selected from the group consisting of diamines, triamines, andtetramines; wherein at least one of said polyurethane prepolymer, saidpolyisocyanate and said curative has its reactive groups blocked by ablocking agent.
 2. The belt of claim 1 wherein said adhesive compositionis further a reaction product of a second polyol, or an oligomericpolyamine.
 3. The belt of claim 1 wherein said adhesive compositionfurther comprises a plasticizer.
 4. The belt of claim 3 wherein saidplasticizer is at least one selected from the group consisting ofphthalates, organo-phosphates, dialkyl-ether di-alkylesters andpolyalkylene-ether di-alkylesters.
 5. The belt of claim 1 wherein saidat least one of said polyurethane prepolymer, said polyisocyanate, andsaid curative is blocked curative complex4,4′-methylenebisdianiline-NaCl.
 6. The belt of claim 1 wherein saidpolyurethane prepolymer is blocked with at least one said blocking agentselected from the group consisting of 3,5-dimethylpyrazole (“DMP”),diethylmalonate (“DEM”), ε-caprolactam (“CAP”), and methyl ethylketoxime (“MEKO”).
 7. The belt of claim 6 wherein said blocking agent isDMP.
 8. The belt of claim 6 wherein said blocking agent is MEKO.
 9. Thebelt of claim 1 wherein said tensile cord comprises carbon fiber.
 10. Amethod of preparing a belt comprising a reinforced elastomeric body,said method comprising: providing a tensile cord impregnated with anadhesive composition comprising the reaction product of; apolyisocyanate and a first polyol or a polyurethane prepolymercomprising said polyisocyanate and said first polyol; and at least onecurative selected from the group consisting of diamines, triamines, andtetramines; wherein at least one of said polyurethane prepolymer, saidpolyisocyanate and said curative has its reactive groups blocked by ablocking agent; and embedding the impregnated tensile cord into theelastomeric body of the belt.
 11. The method of claim 10 wherein saidadhesive composition is applied to said cord in a solvent solution,followed by drying to remove the solvent and the blocking agent.
 12. Themethod of claim 11 further comprising in the impregnating step, using asolution of said polyurethane prepolymer and said curative; and furthercomprising the step of heating to dry said cord after said impregnating.13. The method of claim 12 wherein said step of heating also de-blocksat least a portion of said blocked reactive groups.
 14. The method ofclaim 10 wherein the blocking agent is selected from the groupconsisting of 3,5-dimethylpyrazole (“DMP”), diethylmalonate (“DEM”),ε-caprolactam (“CAP”), and methyl ethyl ketoxime (“MEKO”).
 15. Themethod of claim 14 wherein the blocking agent is DMP.
 16. The method ofclaim 14 wherein the blocking agent is MEKO.
 17. The method of claim 11further comprising the step of preparing an adhesive dip for theimpregnating step by mixing the blocking agent and the prepolymer in anorganic solvent until the prepolymer is blocked; and then adding thecurative.
 18. The belt of claim 1 wherein said polyurethane prepolymercomprises the reaction product of para-phenylene diisocyanate and one ormore polycaprolactone polyols.
 19. The belt of claim 2 wherein saidpolyol is one or more selected from the group consisting ofpolycarbonate polyols and polycaprolactone polyols.
 20. The belt ofclaim 19 wherein said polyol comprises a mixture of a diol and a triol.21. The belt of claim 1 wherein said elastomeric body comprises castpolyurethane elastomer, and said elastomer is in intimate contact withsaid adhesive composition.
 22. The belt of claim 21 wherein said tensilecord comprises a yarn comprising a plurality of carbon fibers withinterstices between said carbon fibers, and wherein said adhesivecomposition impregnates from 20% to 99% of the volume of saidinterstices and coats said carbon fibers; and wherein said elastomerimpregnates at least a portion of the remainder of said interstices. 23.The belt of claim 1 wherein said elastomeric body comprises vulcanizedrubber.
 24. The belt of claim 23 wherein said tensile cord comprises anovercoat adhesive layer disposed between said adhesive composition andsaid vulcanized rubber.
 25. The belt of claim 1 wherein said belt is anendless, power transmission belt.
 26. The belt of claim 25 wherein saidbelt is a toothed belt.
 27. A tensile cord for reinforcing anelastomeric article; with at least a portion of said cord impregnatedwith a polyurea-urethane composition comprising the reaction product of:a polyurethane prepolymer comprising the reaction product of apolyisocyanate and at least one polyol selected from polyester polyols,polycarbonate polyols, and polyether polyols; and a chain extenderselected from diamines, triamines, and tetramines; and wherein thereactive groups of at least one of said prepolymer and said chainextender are blocked with a blocking agent.
 28. The tensile cord ofclaim 27 wherein said tensile cord comprises a filament yarn comprisinga plurality of carbon fibers with interstices between said carbonfibers, and wherein said polyurea-urethane composition impregnates from20% to 99% of the volume of said interstices and coats said carbonfibers.